using System;

namespace Vibstudio.X4NET.Text.Encoding.Core
{
    public class BitPackage
    {
        public static int INDEX_SHIFT_4BITS  = 3;
        public static int INDEX_SHIFT_8BITS  = 2;
        public static int INDEX_SHIFT_16BITS = 1;
        
        public static int SHIFT_MASK_4BITS  = 7;
        public static int SHIFT_MASK_8BITS  = 3;
        public static int SHIFT_MASK_16BITS = 1;
        
        public static int BIT_SHIFT_4BITS  = 2;
        public static int BIT_SHIFT_8BITS  = 3;
        public static int BIT_SHIFT_16BITS = 4;
        
        public static int UNIT_MASK_4BITS  = 0x0000000F;
        public static int UNIT_MASK_8BITS  = 0x000000FF;
        public static int UNIT_MASK_16BITS = 0x0000FFFF;

        private int indexShift;
        private int shiftMask;
        private int bitShift;
        private int unitMask;
        private int[] data;
        
        public BitPackage(int indexShift, int shiftMask,
                int bitShift, int unitMask, int[] data)
        {
            this.indexShift = indexShift;
            this.shiftMask = shiftMask;
            this.bitShift = bitShift;
            this.unitMask = unitMask;
            this.data = data;
        }
        
        public static int Pack16bits(int a, int b)
        {
            return ((b << 16) | a);
        }
        
        public static int Pack8bits(int a, int b, int c, int d)
        {
            return Pack16bits((b << 8) | a, (d << 8) | c);
        }
        
        public static int Pack4bits(int a, int b, int c, int d, 
                                    int e, int f, int g, int h)
        {
            return Pack8bits((b << 4) | a, (d << 4) | c,
                             (f << 4) | e, (h << 4) | g);
        }
        
        public int Unpack(int i)
        {
            return (data[i >> indexShift] >> 
                    ((i & shiftMask) << bitShift)) & unitMask;
        }
   }
}
